Addressing a children's conference in Livingston (page five), Mr Osler said universal pre-school education for three and four-year-olds would ensure the early days in primary were not the first experience of learning in a formal setting.
"The rather gentle and inconvenient (that is to say, for parents) introduction to some primary schools of short days and staggered hours should be reviewed as they make nonsense of continuity in learning," he told the conference, organised by the national steering group for children under the age of eight.
Teachers had to acknowledge that pre-school education would help raise attainment in the early stages of primary and beyond. "If pre-school education is the last new frontier for education, then entry into primary 1 must not be the last fresh start. Primary 1 teachers must build on prior learning," Mr Osler said.
Shelagh Rae, president of the Association of Directors of Education and director in Renfrewshire, said: "With nursery education for four-year-olds,and three-year-olds over the next few years, we could perhaps question whether this gentle lead-in time is necessary and it is legitimate for Mr Osler to question that."
The fresh start in secondary had been criticised and primary teachers had to be aware of similar issues, Mrs Rae said.
Maire Whitehead, vice-president of the Association of Head Teachers in Scotland, said many primaries were already looking at the effects of early intervention. Glasgow recently asked schools about short days but the majority of heads backed the status quo.
Most schools bring in primary 1 pupils for half-days, usually until after the October break.